Semi-Automatic Ground Environment

This article is about the NORAD human-computer interface and the Cold War computer network creating the interface. For the general surveillance radar installations` in each sector, see SAGE radar stations.

*Combat Center not completed since AN/FSQ-8 production was halted c. Nov 1958 when Super Combat Centers were planned[6]:26 with AN/FSQ-32s.
**CC-05 at Hamilton AFB, CA utilized a 3-string AN/GSA-51 computer system and was active from Apr 1/66 to Dec 31/69.

The Semi-Automatic Ground Environment (SAGE) was a system of large computers and associated networking equipment that coordinated data from many radar sites and processed it to produce a single unified image of the airspace over a wide area. SAGE directed and controlled the NORAD response to a Soviet air attack, operating in this role from the late 1950s into the 1980s. Its enormous computers and huge displays remain a part of cold war lore, and a common prop in movies such as Dr. Strangelove and Colossus.

The processing power behind SAGE was supplied by the largest computer ever built, the AN/FSQ-7. Each SAGE Direction Center (DC) housed an FSQ-7 which occupied an entire floor, approximately 22,000 square feet not including supporting equipment. Information was fed to the DC's from a network of radar stations as well as readiness information from various defence sites. The computers, based on the raw radar data, developed "tracks" for the reported targets, and automatically calculated which defences were within range. Operators used light guns to select targets onscreen for further information, select one of the available defences, and issue commands to attack. These commands would then be automatically sent to the defence site via teleprinter.

Connecting the various sites was an enormous network of telephones, modems and teleprinters. Later additions to the system allowed SAGE's tracking data to be sent directly to CIM-10 Bomarc missiles and some of the US Air Force's interceptor aircraft in-flight, directly updating their autopilots to maintain an intercept course without operator intervention. Each DC also forwarded data to a Combat Center (CC) for "supervision of the several sectors within the division"[9] ("each combat center [had] the capability to coordinate defense for the whole nation").[10]:51

SAGE became operational in the late 1950s and early 1960s at a combined cost of billions of dollars. It was noted that the deployment cost more than the Manhattan Project, which it was, in a way, defending against. Throughout its development there were continual questions about its real ability to deal with large attacks, and several tests by Strategic Air Command bombers suggested the system was "leaky". Nevertheless, SAGE was the backbone of NORAD's air defence system into the 1980s, by which time the tube-based FSQ-7's were increasingly costly to maintain and completely outdated. Today the same command and control task is carried out by microcomputers, based on the same basic underlying data.

The AN/FSQ-7 had 100 system consoles, including the OA-1008 Situation Display (SD) with a light gun (at end of cable under plastic museum cover), cigarette lighter, and ash tray (left of the light gun).

Just prior to World War II, Royal Air Force tests with the new Chain Home (CH) radars had demonstrated that relaying information to the fighter aircraft directly from the radar sites was not feasible. The radars determined the map coordinates of the enemy, but could generally not see the fighters at the same time. Even if the information was accurate, it was difficult for the pilots to know where to turn to intercept their targets.

The solution was to send all of the radar information to a central control station where operators collated the reports into single "tracks", and then reported these tracks out to the airbases, or "sectors". The sectors used additional systems to track their own aircraft, plotting both on a single large map. Operators viewing the map could then easily see what direction their fighters would have to fly to approach their targets, and relay that simply by telling them to fly along a certain heading. This Dowding system was the first ground controlled intercept system of large scale, covering the entirety of the UK. It proved enormously successful during the Battle of Britain, and is credited as being a key part in the RAF's success.

However, the system was also slow, often providing information that was up to five minutes out of date. Against propeller driven bombers flying at perhaps 225 miles per hour (362 km/h) this was not a serious concern, but it was clear the system would be of little use against jet powered bombers flying at perhaps 600 miles per hour (970 km/h). The system was also extremely expensive in manpower terms, requiring hundreds of telephone operators, plotters, trackers and all of the radar operators on top of that. This was a serious drain on manpower reserves, making it difficult to expand the network.

The idea of using a computer to handle the task of taking reports and developing tracks had been explored beginning late in the war. By 1944, analog computers had been installed at the CH stations to automatically convert radar readings into map locations, eliminating two people. Meanwhile, the Royal Navy began experimenting with the Comprehensive Display System (CDS), another analog computer that took X and Y locations from a map and automatically generated tracks from repeated inputs. Similar systems began development with the Royal Canadian Navy, DATAR, and the US Navy, the Naval Tactical Data System. A similar system was also specified for the Nike SAM project, specifically referring to a US version of CDS,[11] coordinating the defense over a battle area so that multiple batteries did not fire on a single target. However, all of these systems were relatively small in geographic scale, generally tracking within a city-sized area.

When the Soviets tested RDS-1 in August 1949, the topic of air defense of the US became important for the first time. A study group, the "Air Defense Systems Engineering Committee" was set up under the direction of Dr. George Valley to consider the problem, and is known to history as the Valley Committee.[12]

Their December report noted a key problem in air defense using ground-based radars. A bomber approaching a radar station would detect the signals from the radar long before the reflection off the bomber was strong enough to be detected by the station. The committee suggested that when this occurred, the bomber would descend to low altitude, thereby greatly limiting the radar horizon, allowing the bomber to fly past the station undetected. Although flying at low altitude greatly increased fuel consumption, the team calculated that the bomber would only need to do this for about 10% of its flight, making the fuel penalty easily acceptable.[12]

The only solution to this problem was to build a huge number of stations with overlapping coverage. At that point the problem became one of managing the information. Manual plotting was immediately ruled out as too slow, and a computerized solution was the only possibility. In order to be able to handle this task, the computer would need to be fed information directly, eliminating any manual translation by phone operators, and it would have to be able to analyze that information and automatically develop tracks.[12] A system tasked with defending cities against the predicted future Soviet bomber fleet would have to be dramatically more powerful that the models used in the NTDS or DATAR.[13][14]

The Committee then had to consider whether or not such a computer was even possible. Valley was introduced to Jerome Wiesner, associate director of the Research Laboratory of Electronics at MIT. Wiesner noted that the Servomechanisms Laboratory had already begun development of a machine that might be fast enough for the task. This was the Whirlwind I, originally developed for the Office of Naval Research as a general purpose flight simulator that could simulate any current or future aircraft simply by changing its software.[12]

Wiesner introduced Valley to Whirlwind's project lead, Jay Forrester, who convinced him that Whirlwind was up to the task. In September 1950, an early microwave early-warning radar system at Hanscom Field was connected to Whirlwind using a custom interface developed by Forrester's team. An aircraft was flown past the site, and the system digitized the radar information and successfully sent it to Whirlwind. With this demonstration, the technical concept was proven. Forrester was invited to join the Committee.[12]

With this successful demonstration, Louis Ridenour, chief scientist of the Air Force, wrote a memo stating "It is now apparent that the experimental work necessary to develop, test, and evaluate the systems proposals made by ADSEC will require a substantial amount of laboratory and field effort."[12] Ridenour approached MIT President James Killian with the aim of beginning a development lab similar to the war-era Radiation Laboratory that made enormous progress in radar technology. Killian was initially uninterested, desiring to return the school to its peacetime civilian charter. Ridenour eventually convinced Killian the idea was sound by describing the way the lab would lead to the development of a local electronics industry based on the needs of the lab and the students who would leave the lab to start their own companies. Killian agreed to at least consider the issue, and began Project Charles to consider the size and scope of such a lab.[15]

Project Charles was placed under the direction of Francis Wheeler Loomis and included 28 scientists, about half of whom were already associated with MIT. Their study ran from February to August 1951, and in their final report they stated that "We endorse the concept of a centralized system as proposed by the Air Defense Systems Engineering Committee, and we agree that the central coordinating apparatus of this system should be a high-speed electronic digital computer."[15] The report went on to describe a new lab that would be used for generic technology development for the Air Force, Army and Navy, and would be known as Project Lincoln.[15]

Loomis took over direction of Project Lincoln and began planning by following the lead of the earlier RadLab. By September 1951, only months after the Charles report, Project Lincoln had more than 300 employees. By the end of the summer of 1952 this had risen to 1300, and after another year, 1800. The only building suitable for classified work at that point was Building 22, suitable for a few hundred people at most, although some relief was found by moving the non-classified portions of the project, administration and similar, to Building 20. But this was clearly not enough space, and after considering a variety of suitable locations, a site at Laurence G. Hanscom Field was selected, with the official groundbreaking taking place in 1951.[15]

The terms of the National Security Act were formulated during 1947, leading to the creation of the US Air Force out of the former US Army Air Force. During April of the same year, US Air Force staff were identifying specifically the requirement for the creation of automatic equipment for radar-detection which would relay information to an air defence control system, a system which would function without the inclusion of persons for its operation.[16] The December 1949 "Air Defense Systems Engineering Committee" led by Dr. George Valley had recommended computerized networking[13] for "radar stations guarding the northern air approaches to the United States"[14] (e.g., in Canada). After a January 1950 meeting, Valley and Jay Forrester proposed using the Whirlwind I (completed 1951) for air defense.[citation needed] On August 18, 1950, when the "1954 Interceptor" requirements were issued, the USAF "noted that manual techniques of aircraft warning and control would impose "intolerable" delays"[17]:484 (Air Material Command (AMC) published Electronic Air Defense Environment for 1954 in December .)[2] During February–August 1951 at the new Lincoln Laboratory, the USAF conducted Project Claude which concluded an improved air defense system was needed.[citation needed]

In order to increase the warning time, radar systems called Texas Towers were placed out in the Atlantic Ocean using technology similar to Texas-style offshore oil platforms

In a test for the U.S. military at Bedford on 20 April 1951, data produced by a radar was transmitted through telephone lines to a computer for the first time, showing the detection of a mock enemy aircraft. This first test was directed by C. Robert Wieser.[16]

The "Summer Study Group" of scientists in 1952 recommended "computerized air direction centers…to be ready by 1954."[18]

IBM's "Project High" assisted under their October 1952 Whirlwind subcontract with Lincoln Laboratory,[19]:210 and a 1952 USAF Project Lincoln "fullscale study" of "a large scale integrated ground control system" resulted in the SAGE approval "first on a trial basis in 1953".[20]:128 The USAF had decided by April 10, 1953, to cancel the competing ADIS (based on CDS), and the University of Michigan’s Aeronautical Research Center withdrew in the spring.[21]:289Air Research and Development Command (ARDC) planned to "finalize a production contract for the Lincoln Transition System".[4]:201 Similarly, the July 22, 1953, report by the Bull Committee (NSC 159) identified completing the Mid-Canada Line radars as the top priority and "on a second-priority-basis: the Lincoln automated system"[22] (the decision to control Bomarc with the automated system was also in 1953.)[23]

The Priority Permanent System with the initial (priority) radar stations was completed in 1952[4]:223 as a "manual air defense system"[7] (e.g., NORAD/ADC used a "Plexiglas plotting board" at the Ent command center.) The Permanent System radar stations included 3 subsequent phases of deployments and by June 30, 1957, had 119 "Fixed CONUS" radars, 29 "Gap-filler low altitude" radars, and 23 control centers".[24] At "the end of 1957, ADC operated 182 radar stations [and] 17 control centers … 32 [stations] had been added during the last half of the year as low-altitude, unmanned gap-filler radars. The total consisted of 47 gap-filler stations, 75 Permanent System radars, 39 semimobile radars, 19 Pinetree stations,…1 Lashup -era radar and a single Texas Tower".[4]:223 "On 31 December 1958, USAF ADC had 187 operational land-based radar stations" (74 were "P-sites", 29 "M-sites", 13 "SM-sites", & 68 "ZI Gap Fillers").[6]

Jay Forrester was instrumental in directing the development of the key concept of an interception system during his work at Servomechanisms Laboratory of MIT. The concept of the system, according to the Lincoln Laboratory site was to:[25]

develop a digital computer that could receive vast quantities of data from multiple radars and perform real-time processing to produce targeting information for intercepting aircraft and missiles

The AN/FSQ-7 was developed by the Lincoln Laboratory's Digital Computer Laboratory and Division 6, working closely with IBM as the manufacturer. Each FSQ-7 actually consisted of two nearly identical computers operating in "duplex"[26] for redundancy. The design used an improved version of the Whirlwind I magnetic core memory and was an extension of the Whirlwind II computer program, renamed AN/FSQ-7 in 1953 to comply with Air Force nomenclature. It has been suggested the FSQ-7 was based on the IBM 701 but, while the 701 was investigated by MIT engineers, its design was ultimately rejected due to high error rates and generally being "inadequate to the task."[27] IBM's contributions were essential to the success of the FSQ-7 but IBM benefited immensely from its association with the SAGE project, most evidently during development of the IBM 704.[28][29]

On October 28, 1953, the Air Force Council recommended 1955 funding for "ADC to convert to the Lincoln automated system"[4]:193 ("redesignated the SAGE System in 1954").[4]:201 The "experimental SAGE subsector, located in Lexington, Mass., was completed in 1955…with a prototype AN/FSQ-7…known as XD-1"[9] (single computer system[30] in Building F).[21] In 1955, Air Force personnel began IBM training at the Kingston, New York, prototype facility,[5] and the "4620th Air Defense Wing (experimental SAGE) was established at Lincoln Laboratory"

In 1957, SAGE System groundbreaking at McChord AFB was for DC-12[35] where the "electronic brain" began arriving in November 1958,[36] and the "first SAGE regional battle post [CC-01] began operating in Syracuse, New York in early 1959".[4]:263 BOMARC "crew training was activated January 1, 1958",[37] and AT&T "hardened many of its switching centers, putting them in deep underground bunkers",[38] The North American Defense Objectives Plan (NADOP 59-63) submitted to Canada in December 1958 scheduled 5 Direction Centers and 1 Combat Center to be complete in Fiscal Year 1959, 12 DCs and 3 CCs complete at the end of FY 60, 19 DC/4 CC FY 61, 25/6 FY 62, and 30/10 FY 63.[6] On June 30 NORAD ordered that "Air Defense Sectors (SAGE) were to be designated as NORAD sectors",[39] (the military reorganization had begun when effective April 1, 1958, CONAD "designated four SAGE sectors -- New York, Boston, Syracuse, and Washington -- as CONAD Sectors".)[34]:7

On "June 26, 1958,…the New York sector became operational"[4]:207 and on December 1, 1958, the Syracuse sector's DC-03 was operational ("the SAGE system [did not] become operational until January 1959.")[24] Construction of CFB North Bay in Canada was started in 1959 for a bunker ~700 feet (210 m) underground (operational October 1, 1963),[48] and by 1963 the system had 3 Combat Centers. The 23 SAGE centers included 1 in Canada,[49] and the "SAGE control centers reached their full 22 site deployments in 1961 (out of 46 originally planned)."[50] The completed Minot AFB blockhouse never received an AN/FSQ-7 (the April 1, 1959, Minot Air Defense Sector consolidated with the Grand Forks ADS on March 1, 1963).[citation needed]

The Subsector Command Post ("blue room") had personnel on the DC's 3rd floor and a Display and Warning Light System for the operator environment, e.g., Large Board Projection Equipment projecting from the 4th floor[5] (top, Cape Cod shown on 3rd/4th floor wall)[where?] and Command Post Digital Display Desk[51] (center, with operators)

The environment allowed radar station personnel to monitor the radar data and systems' status (e.g., Arctic Tower radome pressure) and to use the range height equipment to process height requests from Direction Center (DC) personnel. DCs received the Long Range Radar Input from the sector's radar stations, and DC personnel monitored the radar tracks and IFF data provided by the stations, requested height-finder radar data on targets, and monitored the computer's evaluation of which fighter aircraft or Bomarc missile site could reach the threat first. The DC's "NORAD sector commander's operational staff"[52] could designate fighter intercept of a target or, using the Senior Director's keyed console[53] in the Weapons Direction room,[5] launch a Bomarc intercept with automatic Q-7 guidance of the surface-to-air missile to a final homing dive (equipped fighters eventually were automatically guided to intercepts).

The "NORAD sector direction center (NSDC) [also had] air defense artillery director (ADAD) consoles [and an Army] ADA battle staff officer", and the NSDC automatically communicated crosstelling of "SAGE reference track data" to/from adjacent sectors' DCs and to 10 NikeMissile MasterAADCPs.[52] Forwardtelling automatically communicated data from multiple DCs to a 3-story Combat Center (CC) usually at one of the sector's DCs[9] (cf. planned Hamilton AFB CC-05 near the Beale AFB DC-18) for coordinating the air battle in the NORAD region (multiple sectors) and which forwarded data to the NORAD Command Center (Ent AFB, 1963 Chidlaw Building, & 1966 Cheyenne Mountain). NORAD's integration of air warning data (at the ADOC) along with space surveillance, intelligence, and other data allowed attack assessment of an Air Defense Emergency for alerting the SAC command centers (465L SACCS nodes at Offutt AFB & The Notch), The Pentagon/Raven RockNMCC/ANMCC, and the public via CONELRAD radio stations.

The SAGE network of computers connected by a "Digital Radar Relay"[60] (SAGE data system)[61] used AT&T voice lines, microwave towers, switching centers (e.g., SAGE NNX 764 was at Delta, Utah[62] & 759 at Mounds, Oklahoma[63]), etc.; and AT&T's "main underground station" was in Kansas (Fairview) with other bunkers in Connecticut (Cheshire), California (Santa Rosa), Iowa (Boone)[64] and Maryland (Hearthstone Mountain). CDTS modems at automated radar stations transmitted range and azimuth,[65] and the Air Movements Identification Service (AMIS) provided air traffic data to the SAGE System.[66] Radar tracks by telephone calls (e.g., from Manual Control Centers in the Albuquerque, Minot, and Oklahoma City sectors) could be entered via consoles of the 4th floor "Manual Inputs" room adjacent to the "Communication Recording-Monitoring and VHF" room.[67] In 1966, SAGE communications were integrated into the AUTOVON Network.[63]

SAGE Sector Warning Networks (cf. NORAD Division Warning Networks) provided the radar netting communications for each DC[6] and eventually also allowed transfer of command guidance to autopilots of TDDL-equipped interceptors for vectoring to targets[40] via the Ground to Air Data Link Subsystem and the Ground Air Transmit Receive (GATR) network of radio sites for "HF/VHF/UHF voice & TDDL"[62] each generally co-located at a CDTS site. SAGE Direction Centers and Combat Centers were also nodes of NORAD's Alert Network Number 1, and SAC Emergency War Order Traffic[68] included "Positive Control/Noah's Ark instructions" through northern NORAD radio sites to confirm or recall SAC bombers if "SAC decided to launch the alert force before receiving an execution order from the JCS".[6]

A SAGE System ergonomic test at Luke AFB in 1964 "showed conclusively that the wrong timing of human and technical operations was leading to frequent truncation of the flight path tracking system" (Harold Sackman).[47]:9 SAGE software development was "grossly underestimated"[21]:370 (60,000 lines in September 1955):[69] "the biggest mistake [of] the SAGE computer program was [underestimating the] jump from the 35,000 [WWI] instructions … to the more than 100,000 instructions on the" AN/FSQ-8.[70] NORAD conducted a Sage/Missile Master Integration/ECM-ECCM Test in 1963,[71] and although SAGE used AMIS input of air traffic information, the 1959 plan developed by the July 1958 USAF Air Defense Systems Integration Division[6] for SAGE Air Traffic Integration (SATIN) was cancelled by the DoD.[72]

SAGE histories include a 1983 special issue of the Annals of the History of Computing,[81] and various personal histories were published, e.g., Valley in 1985[82] and Jacobs in 1986.[83] In 1998, the SAGE System was identified as 1 of 4 "Monumental Projects",[84] and a SAGE lecture presented the vintage film In Your Defense followed by anecdotal information from Les Earnest, Jim Wong, and Paul Edwards.[30] In 2013, a copy of a 1950s cover girl image programmed for SAGE display was identified as the "earliest known figurative computer art".[5] Company histories identifying employees' roles in SAGE include the 1981 System Builders: The Story of SDC[85] and the 1998 Architects of Information Advantage: The MITRE Corporation Since 1958.[86]

^ abcdefghijklmPreface by Buss, L. H. (Director) (14 April 1959). North American Air Defense Command and Continental Air Defense Command Historical Summary: July–December 1958 (Report). Directorate of Command History: Office of Information Services. "USAF also set down a new schedule (see table preceding). This schedule was to be included in an entirely new SAGE schedule (Schedule A) to be prepared by the SAGE Project Office. The phasing was to be as follows. The last combat center, AN/FSQ-8, to be installed under SAGE Schedule 7 (Improved), was to be at McChord AFB (25th Air Division). Subsequent combat facilities and equipment were to be cancelled with the exception of (1) one AN/FSQ-8 that was to be converted to an AN/FSQ-7, using FY 1959 funds, to be installed at the Sioux City DC, and (2) the combat center building at Minot." (improved) On April 1, 1966, Combat Center CC-03 at McChord AFB, WA was inactivated in conjunction with the activation of Combat Center CC-05 at Hamilton AFB, CA, and the combining of 25th, 26th and 27th NORAD divisions into the new Headquarters Western NORAD Region at HAFB. CC-05 utilized a 3-String AN/GSA-51 computer system. CC-05 and Headquarters Western NORAD Region were inactivated at Hamilton AFB on December 31, 1969.

^ abcdColonel John Morton (narrator). In Your Defense(digitized movie). Western Electric. Retrieved 2012-04-03. The System Development Corporation…in the design of massive computer programs … Burroughs…electronic equipment … Western Electric…assist the Air Force in coordinating and managing the entire effort…and design of buildings. …SAGE project office…Air Material Command[when?]

^ abc"Overview |". SAGE: The First [computerized] National Air Defense Network. IBM.com. Retrieved 2013-05-08. the AN/FSQ-7…was developed, built and maintained by IBM. … In June 1956, IBM delivered the prototype of the computer to be used in SAGE.

^ abc"Introduction". Ed-Thelen.org. The function of the Control Center in solving the air defense problem is to combine, summarize, and display the air battle picture for the supervision of the several sectors within the division. … The typical Control Center (CC) building housing the AN/FSQ-8 Combat Control Central is a 3-story structure of the same type construction as the DC building. (p. 7)

^Futrell, Robert Frank (June 1971). Ideas, Concepts, Doctrine: A History of Basic Thinking in the United States Air Force 1907–1964 (Report). Volume 1. Aerospace Studies Institute, Air University. (cited by Volume I p. 187)

^McVeigh, D. R. (January 1956). The Development of the Bomarc Guided Missile 1950–1953 (Report). Western Air Development Center. (cited by Volume I p. 108 footnote 69: "Before the end of 1953, it was also decided that the Sage system being developed by Lincoln Laboratories would be used to control the Bomarc.69")

^ abCondit, Kenneth W. (1992) [1971 classified vol]. "Chapter 15: Continental Defense". The Joint Chiefs of Staff and National Policy: 1955–1956 (Report). Volume VI of History of the Joint Chiefs of Staff. Washington, D.C.: Historical Office, Joint Staff. p. 268 Major elements to be developed to a high state of readiness by the beginning of 1957 included the Distant Early Warning (DEW) Line and an air defense control system employing semiautomatic control centers.1 … At the beginning of 1955, the radar warning systems consisted of 83 permanent radars in the United States, 33 permanent radars of the Pine Tree system in Canada, 12 permanent radars in Alaska, and six shipborne radars stationed off the east coast of the United States. … To facilitate CONAD's job of absorbing data from warning radars and feeding the appropriate instructions to interceptor and antiaircraft forces, the Air Force had sponsored the development of the Semi-Automatic Ground Environment (SAGE) system by the Lincoln Laboratory of the Massachusetts Institute of Technology. The SAGE system was adopted but was not to become operational until January 1959. … the DEW Line…became operational shortly afterward, on 13 Aug 57. … Chapter 15. Continental Defense 1. NSC 5408, 24 Feb 54, CCS 381 US (5-23-46) sec 37. (Condit includes detailed numbers of 1954, 1956, and 1957 radar stations on p. 269 Table 13.)

^ abcd"Vigilance and Vacuum Tubes: The SAGE System 1956-63"(SAGE Talk Transcript). Ed-Thelen.org. 1998. Retrieved 2013-02-16. the Whirlwind computer, which was a digital version of the ASCA, was about five million dollars, in 1950’s [sic] dollars … For the 1949 fiscal year, MIT requested 1.5 million dollars for the Whirlwind project. … one [SAGE computer] was at Lincoln Lab, …the XD-1, and the other one was at Kingston, the XD-2. So we used both those sites for development. … The XD-1 was a simplex system…not duplex … the original vacuum-tube computers—the last one was finally taken down in 1983, still operating. … IBM got…about 500 million dollars…to build the 56 computers.

^"SAGE: The New Aerial Defense System of the United States". The Military Engineer. Mar–Apr 1956. (cited by Schaffel pp. 311, 332)

^ abcdPreface by Buss, L. H. (Director) (1 October 1958). North American Air Defense Command Historical Summary: January–June 1958 (Report). Directorate of Command History: Office of Information Services. Directorate of Command History: Office of Information Services; p. 21: "DC's, and CC's, which were to screen and evaluate the reports before forwarding to NORAD headquarters. ALERT NETWORK NUMBER 1 On 1 July 1958, a new Alert # 1 network was placed in operation (the old network was to remain in operation as a back-up until 1 August 1958). The new network connected NORAD on 1 July 1958 with 33 Stations that required air defense alert and warning information. This included such agencies as major commands, air divisions, regions, and the USAF Command Post. Only 29 of the stations operating on 1 July were both transmit and receive stations, the other four (TAC Headquarters, Sandia Base, ADCC (Blue Ridge Summit), and the Presidio at San Francisco) were receive-only stations. …the new system…gave NORAD the ability to tell which station received its alert messages and which did not. The new system also had two master stations -- NORAD [at Ent AFB] and the ALCOP at Richards-Gebaur AFB. This feature permitted the ALCOP to continue operations of the network and carry on with the alert procedures should NORAD become a war casualty."

^ abcIsrael, David. R. (January 1965). System Design and Engineering for Real-Time Military Data Processing Systems(AD610392, Technical Documentary Report ESD-TDR-64-168, SR-124) (Report). Bedford, Massachusetts: The MITRE Corporation. Retrieved 2013-04-20. To be more specific, I have in mind something like the BADGE system; in U.S. experience, examples would be SAGE, 412L,[specify] or the NORAD COC … The early development of SAGE was hampered by the fact that the radars were not considered as a part of the system.

^Benington, Herbert D. Production of Large Computer Programs(PDF) (adaptation of June 1956 presentation). Retrieved February 18, 2015. The following paper is a description of the organization and techniques we used at MIT's Lincoln Laboratory in the mid-1950s to produce programs for the SAGE air-defense system. The paper appeared a year before the announcement of SAGE; no mention was made of the specific application other than to indicate that the program was used in a large control system. The programming effort was very large—eventually, close to half a million computer instructions. About one-quarter of these instructions supported actual operational air-defense missions. … In a letter to me on April 23, 1981 … A Lincoln Utility System of service routines containing 40,000 instructions has been prepared … the experience of the Lincoln Laboratory that a system of service programs equal in size to the main system program must be maintained to support preparation, testing, and maintenance of the latter.

^Edwards, Paul N (1997). The Closed World: Computers and the Politics of Discourse in Cold War America(Google Books). ISBN9780262550284. SAGE—Air Force project 416L—became the pattern for at least twenty-five other major military command-control systems… These were the so-called "Big L" systems [and] included 425L, the NORAD system; 438L, the Air Force Intelligence Data Handling System; and 474L, the Ballistic Missile Early Warning System (BMEWS). … Project 465L, the SAC Control System (SACCS) [with] over a million lines, reached four times the size of the SAGE code and consumed 1,400 man-years of programming; SDC invented a major computer language, JOVIAL, specifically for this project.

^Benington, Herbert D. Foreword: Production of Large Computer Programs(PDF) (Report). Retrieved February 18, 2015. (Foreword is part of pdf that includes "Editor's Note" and a transcript of Benington's 1956 symposium paper beginning with the Introduction—"This paper looks ahead at some programming problems that are likely to arise during Forrester's 1960-1965 period of real-time control applications."—through Summary: "The techniques that have been developed for automatic programming over the past five years have mostly aimed at simplifying the part of programming that, at first glance, seems toughest—program input, or conversion from programmer language to machine code.")

^Missile Master Plan [1][2]; identified by Schaffel p. 260: "…the Defense Department to issue, on June 19, 1959, the Master Air Defense Plan. [sic] Key features of the plan included a reduction in BOMARC squadrons, cancellation of plans to upgrade the interceptor force, and a new austere SAGE program. In addition, funds were deleted for gap-filler and frequency-agility radars.21 [1959 NORAD/CONAD Hist Summary: Jan-Jun]"

^Proposed IAO/DTE Resource Availability (Report). 1970 [circa]. An Air Force radar facility at Tonopah, Nevada is being released by the Air Force to the Federal Aviation Agency. … ADC has a BUIC III radar facility installed and operating at Fallon. This semi-automated ground environment system permits several other radars to be tied into it.

^Baum, Claud (1981). System Builders: The Story of SDC. Santa Monica: System Development Corporation. (cited by Schaffel p. 205/311: "Although technically a Lincoln unit, SDC did much of its work at RAND Headquarters in Santa Monica, California. RAND designers developed the Model I software that allowed realistic training for [SAGE] technicians scheduled to operate the first direction center.")